Bombardments likely enhanced conditions for life on Mars, study finds

An image of the surface of Mars which was battered by comets and asteroids 4 billion years ago.

Story highlights

  • Study: Mars was hit by large comets and asteroids some 4 billion years ago
  • This likely enhanced climate conditions to make the planet more conducive to life
  • The study was done by the University of Colorado at Boulder

(CNN)It could be another tantalizing clue in the search for life beyond Earth. Picture this:

It's some 4 billion years ago.
    Earth, and Mars, which formed around the same time in the solar system, have been in existence for roughly 500 million years.
    Mars is pummeled by gigantic comets and asteroids hundreds of kilometers wide -- some as big as West Virginia or Latvia.
    The collisions generate tremendous heat, melting subsurface ice on the cold, dry planet and enhancing the climate enough to make Mars more conducive to life, at least for a while.
    This is the one of the findings in a new study by the University of Colorado-Boulder.
    "The running line is if there was life on early Mars, this ancient bombardment was highly beneficial to it," said Stephen Mojzsis, a professor in the university's geological sciences department and the co-author of the report.
    "Most people think that asteroids extinguish life, but the opposite is true for life -- life as we know it -- microbial life," the professor said.

    Yellowstone Park annex

    The massive impacts would have produced regional hydrothermal systems much such as those in Yellowstone National Park, which harbors chemically powered microbes, he said. It could have also temporarily increased Mars' atmospheric pressure, heating the planet enough to "restart" a dormant water cycle, he said.
    Scientists have long known there was once running water on Mars, as evidenced by ancient river valleys, deltas and parts of lake beds.
    A few years ago, the Mars Curiosity rover detected methane gas and other organic matter on the surface of Mars, suggesting the possibility of past or present life. Scientists are not sure whether the building blocks of life were formed on Mars or brought to the planet by meteorites.
    Much of this collision action on Mars happened during a period known as the Late Heavy Bombardment about 3.9 billion years ago, Mojzsis said, when the developing solar system was a shooting gallery of comets, asteroids, moons and planets.
    "What really saved the day for Earth was its oceans," Mojzsis said. "In order to eradicate life on Earth, the oceans would have had to have been boiled away... and that is exceedingly difficult."
    "What you need for life to get started on a planet is water to be on the surface for an extended time, for tens of millions of years," said Richard Zurek, Chief Scientist at the Mars program office at the Jet Propulsion Lab in Pasadena.

    How long did it last?

    He said impact heating would have warmed the surface but the question is this: How long did it last given what we see today in Mars with its thin atmosphere and a cold climate? The new study suggests it did not last long enough -- maybe a few million years.
    NASA missions are continuing to look for evidence - bio-signatures - that life did develop on Mars.
    "There still may be life on Mars -- life did not evolve to something that could survive on the surface, but there is still a possibility that life could be in microbes on the crust of Mars... We don't know if life died out, we don't know if it started, it is still wide open."